Echo vulnerable to Reflected Cross-Site Scripting (XSS) via unsanitized JSONP callback in Context.JSONP / Context.JSONPBlob
CVE-2026-118652
Summary The Context.JSONP, Context.JSONPBlob, and internal jsonPBlob helper in context.go directly concatenate the caller-supplied callback parameter into a JavaScript response without any validation, escaping, or allow-listing. This creates a high-impact reflected XSS that can be triggered by any route passing attacker-controlled data (query string, form, header, path param, etc.) into the callback. Present in current master and v5.1.0 (latest release). Vulnerable Code (verbatim) go func (c Context) jsonPBlob(code int, callback string, i any) (err error) { c.writeContentType(MIMEApplicationJavaScriptCharsetUTF8) c.response.WriteHeader(code) if , err = c.response.Write([]byte(callback + "(")); err != nil { return } if err = c.echo.JSONSerializer.Serialize(c, i, ""); err != nil { return } if , err = c.response.Write([]byte(");")); err != nil { return } return } func (c Context) JSONP(code int, callback string, i any) (err error) { return c.jsonPBlob(code, callback, i) } func (c Context) JSONPBlob(code int, callback string, b []byte) (err error) { c.writeContentType(MIMEApplicationJavaScriptCharsetUTF8) c.response.WriteHeader(code) if , err = c.response.Write([]byte(callback +…
Assessment
- CVSS
- 6.1 (v3.1)
- Severity
- Medium
- EPSS
- 0.00239% chance of exploitation in the next 30 days
- Known exploited
- Not listed in CISA KEV
- Exploit availability
- Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
- Published
- 28 October 2026
- Last updated
- 28 October 2026
- Affected
- go · github.com/labstack/echo/v5, github.com/labstack/echo/v4
- Weakness
- CWE-79
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
At the source
References
- https://github.com/labstack/echo/security/advisories/GHSA-h9g5-28mm-hx3g
- https://github.com/labstack/echo/commit/b838391e2eade87ae7e5a09d7bb5087bec271ec1
- https://github.com/labstack/echo/commit/fc410094b2f3415cf2bf5204082137b205bfd5af
- https://github.com/labstack/echo/releases/tag/v4.16.0
- https://github.com/labstack/echo/releases/tag/v5.4.0
- https://github.com/advisories/GHSA-h9g5-28mm-hx3g
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